Frosting won't thicken

I have made frosting like this before. I think the trick is to actually chill the milk mixture (and then peel any skin that forms on top, otherwise you get lumps)!

Sounds like you just have to go in and try it again with letting the milk cool completely.

It will thicken back up some after cooling, but now that you have melted the butter it will be grainy, just so you are prepared for tomorrow morning. The cooked flour mixture has to be completely cooled before beating it into the butter sugar mixture.

The thickened milk must be cooled off or the butter will melt. Try salvaging by putting the whole thing in the forgot cool and then beat again. Maybe that will salvage it.

Dear WannaBeBaker – The icing you are referring to in your question, is what my Mother referred to as a “Cooked Icing”. It was very common in the PA Dutch Country, where I grew up. Many local cookbooks often had a recipe for the rich creamy frosting. The key to success with this frosting are rather simple, once learned. First, the flour and milk (1/2 & ½ - better!); this must be cooked over medium heat, stirring constantly, for about 3-5 minutes or until mixture thickens and comes to a boil. Once a boil is reached, it must boil for an additional 1 minute. Then, just like with a cooked pudding, cover the flour/milk mixtures warm surface with plastic food wrap; (directly in contact with mixture – no air gap) cool completely. Once cooled to room temperature, or cooler – proceed with the icing recipe. Guarantee you will have success from there!

I wonder if you added the warm milk/flour mixture too quickly and melted the butter/shortening. The recipe I use says to add the milk mixture 1 TB at a time. The other thing that sort puzzles me is the shortening. Most recipes that I have read for this frosting only uses butter, 1 cup, for that much milk and flour.
This is my favorite white frosting. It's smooth, satiny with just the right amount of sweetness that is not achingly sweet. I've seen it called Miracle frosting, Ermine frosting, boiled milk frosting. I suggest looking at other recipes because you really don't need the shortening to make this fantastic frosting.

Yeah, I did wonder about it. I let the milk cool for about 15 minutes, and it didn't feel hot when I dipped my pinky finger in after mixing it up, but maybe not warm is not cool enough? I tried adding some powdered sugar, which did help thicken it up somewhat, but I've got it in the fridge now to see if that will help thicken it up more. I can ice the cupcakes tomorrow morning - here's hoping a night in the fridge solves my problems!

I've never made a frosting like this, but it sounds like the hot milk may have melted the butter and shortening. I would try chilling until stiff and then whipping again.